1. Field of the Invention
The present invention relates to a magnetic disk unit used as an external storage for an information processor such as a computer to a method of detecting contact between a magnetic head slider and a magnetic disk, and to a device for detecting such contact.
2. Description of the Related Art
Heretofore, for a method of detecting contact between a magnetic head slider and a magnetic disk, a method of using an acoustic emission (AE) sensor is known as disclosed in Japanese published unexamined patent application No. Sho61-32278. The above patent application discloses a magnetic head provided with an AE sensor for detecting contact between a magnetic head slider and a magnetic disk surface that prevents the disk surface from being damaged by moving the magnetic head slider to a landing zone or stopping the rotation of a disk after the contact is detected.
The AE sensor described in the above patent application is mainly used for detecting contact between the slider and the disk depending upon whether magnetic powder and others exist or not. The above patent application also discloses preventing recorded information from being destroyed by operating a protection network when the AE sensor detects the contact.
A method of detecting contact using a contact sensor typified by an AE sensor is certainly an effective method in relation to verifying contact between a magnetic head slider and a magnetic disk. However, it is difficult to apply the above method of detecting contact using a contact sensor to an actual magnetic disk unit because a small-sized magnetic disk unit has (1) a problem of installed space, (2) a problem of a cost when a piezoelectric element is built in a slider to solve the above problem of space, (3) a problem of the wiring of a fine wire for a contact sensor, (4) a problem that another circuit is required for the contact sensor and others.
For a method of solving the above problems, Japanese published unexamined patent application No. H1-100779 discloses a detecting method based upon the output of a signal when a magnetic head and a magnetic disk come in contact so as to obtain a magnetic disk unit wherein recorded information can be effectively prevented from being destroyed when the magnetic head detects contact with the magnetic disk. In the above detecting method, contact between a magnetic head and a magnetic disk is detected by detecting fluctuation larger than the predetermined one of a signal output from the magnetic head. A signal output from the magnetic head greatly fluctuates when the magnetic head and the magnetic disk come in contact. That is, in the above patent application, the output voltage of a magnetic head is amplified by an amplifier, is input to a rectifying circuit via an impedance conversion circuit and rectified, is further smoothed by a time constant circuit and the collapse below a fixed level of the signal is detected by a comparison circuit.
However, in the above conventional type magnetic disk unit, though the above problem of the AE sensor can be solved based upon the output of a signal, contact cannot be judged only based upon the fluctuation of output because fluctuation due to an attachment on the surface of the magnetic head slider, the waviness of the medium and others is included in the fluctuation of output. Because the fluctuation of output due to contact between the magnetic head slider and the magnetic disk is extremely small, while the fluctuation due to an attachment on the surface of the magnetic head slider, the waviness of the medium and others is very large.
Therefore, there is a problem that contact cannot precisely be judged by contact judging means disclosed in the above Japanese published unexamined patent application No. H1-100779, compared with judgment based upon acoustic emission and abrasion caused by contact is considerably in progress when contact between the magnetic head slider and the magnetic disk is indicated.
As described above, the above related art has the following problems:
The first problem is that if contact is detected as the fluctuation exceeding predetermined fluctuation of an envelope output signal (a read output signal of a magnetic head), change exceeding the amplitude of the fluctuation of an envelope caused by an attachment on the surface of a magnetic head slider, the waviness of a magnetic disk and others is required and therefore, if change is included in the above amplitude of the fluctuation of an envelope, contact cannot be detected. Particularly, the fluctuation of output in the start of contact is extremely small, compared with the fluctuation of output due to and the waviness of a medium and an attachment on the surface of a magnetic head slider and contact cannot be judged.
Therefore, the realization of a method of solving these problems and detecting contact at great sensitivity is desired.
The second problem is that in conventional type measuring technique by a contact sensor typified by an AE sensor, an AE sensor is required to be fixed, a method of wiring an output line is complicated in addition to the increase of mobile weight, further, an amplifier for a contact sensor is required to be installed and an apparatus is complicated and high-priced to compact the above devices.
For the reason, it can be given that the output of an AE sensor is very small, it is very difficult to detect the change of a signal without an amplifier and the increase of mobile weight requires the change of design because of the miniaturization and the reduction in weight of a magnetic head slider.
An AE sensor can detect contact between a magnetic head and a magnetic disk at great sensitivity, however, it has the problems shown in the above items (1) to (4) and others.
Therefore, the establishment of a contact detecting method provided with sensitivity equal to the sensitivity of an AE sensor is desired.
As described above, for a method of detecting contact between a magnetic disk and a magnetic head slider, a detecting method using a contact sensor typified by an AE sensor is typical and contact can be certainly detected at great sensitivity according to the above contact detecting method by a contact sensor, however, from the viewpoint of a magnetic disk unit as described above, the above contact detecting method has a problem that the method is not realistic. Therefore, the establishment of a contact detecting method from the viewpoint of a magnetic disk unit is desired.